Vegetable oils such as rapeseed oil and high oleic varieties of oils are considered to be potential candidates to prepare bio-lubricant feed stocks which replace conventional mineral oil based lubricating oils and synthetic esters [Randles, S. J. et al.; J. Synthetic Lubrication., 9:145 (1992); Asadauskas, S. et al.; Lub. Eng., 52:877 (1996)]. Vegetable oil-based derivatives are attractive alternatives to petroleum derived products because they have enhanced biodegradability, lower toxicity and they originate from renewable oilseed sources. The ester linkages deliver inherent lubricity and enable the oils to adhere to metal surfaces. In addition, vegetable oils have higher solubilising capacity for contaminants and additives than mineral oil base fluids. Most of the work reported on lubricant base stocks in the literature is based on edible oils.
A major non-edible oil namely castor oil serves as an industrial raw material for the manufacture of a number of functional derivatives [J. Am. Oil Chem. Soc. 51, 65 (1974), J. Am. Oil Chem. Soc. 48, 759 (1971)]. Castor oil is a well known lubricant due to the presence of hydroxyl fatty acid (12-Hydroxy 9 cis-octadecenoic acid or ricinoleic acid) to an extent of 85-90% (Chemical Business, 1991, 55-60). J. Synthetic Lubrication 24,181 (2007) reported the physico-chemical characteristics of castor oil.
Castor oil has undesirable very high viscosity at 40° C. as well as at 100° C. castor oil also gets dehydrated at temperature of about 200° C. and above.
The rheological characteristics of chemically modified castor oil are much better than mineral oil and other plant oils based lubricants. Castor oil based esters with hydroxyl group at position 12 esterified with C6, C12, C16 and C18 fatty acids are of interest, mainly due to their physical characteristics at low temperature (Eur J Lipid Sci. Technol. 2003, 105, 214-218). Esters with a free hydroxyl group are efficient in improving the lubrication ability of petroleum fuels. Methyl and ethyl esters of ricinoleic and 12-hydroxy octadecanoic acids were prepared and their physico-chemical properties were determined and the results suggested that with the exception of the viscosity, density and cetane number the presence of free hydroxyl group had no influence on their parameters and does not limit the use of their esters as fuels (Eur J. lipid Sci. Technol., 2006, 108, 629-635). Soybean oil was modified to convert sites of unsaturation to C2 to C10 diesters which have utility as hydraulic fluids, metal working fluids and other industrial fluids (U.S. Pat. No. 6,583,302). There were no reports on the preparation of derivatives of these tri hydroxy fatty acid rich mixture for their usefulness as lubricant base stocks.